This invention is generally directed to improved overcoated layered photoresponsive devices, and more specifically, the present invention is directed to an improved layered photoresponsive device containing as electron transporting materials novel derivatives of fluorenylidene methane. In one specific embodiment of the present invention there is provided a layered photoresponsive device containing a photogenerating layer, and in contact therewith an electron transporting layer comprised of certain derivatives of 9-fluorenylidene methane compositions dispersed in an inactive resinous binder material. Additionally, the present invention includes within the scope thereof photoresponsive devices wherein the electron transporting layer selected has added thereto, or is doped with suitable electron donor molecules to improve the physical and/or electrical properties thereof. The improved photoresponsive devices of the present invention are useful for incorporation into various imaging systems, particularly electrostatographic imaging systems, wherein for example the device is initially charged positively.
The formation and development of electrostatic latent images on the imaging surfaces of photoconductive materials by electrostatic means is well known, one such method involving the formation of an electrostatic latent image on the surface of a photosensitive plate, referred to in the art as a photoreceptor. This photoreceptor is generally comprised of a conductive substrate containing on its surface a layer of photoconductive material, and in many instances a thin barrier layer is situated between the substrate and the photoconductive layer to prevent charge injection from the substrate, which injection could adversely affect the quality of the images generated.
Numerous different xerographic photoconductive members are known including, for example, a homogeneous layer of a single material, such as vitreous selenium, or a composite layered device containing a dispersion of a photoconductive composition. An example of one type of composite xerographic photoconductive member is described, for example, in U.S. Pat. No. 3,121,006 wherein there is disclosed finely divided particles of a photocondutive inorganic compound dispersed in an electrically insulating organic resinous binder. In a commercial form the binder layer contains particles of zinc oxide uniformly dispersed in a resinous binder, and coated on a paper backing. The binder material as disclosed in this patent comprises a composition which is incapable of transporting for any significant distance injected charge carriers generated by the photoconductive particles. Illustrative examples of specific binder materials disclosed include for example polycarbonate resins, polyester resins, polyamide resins, and the like.
There are also known photoreceptor material comprised of other inorganic or organic materials wherein the charge carrier generation and charge carrier transport functions are accomplished by discrete contiguous layers. Additionally, layered photoreceptor materials are disclosed in the prior art which include an overcoating layer of an electrically insulating polymeric material. However, the art of xerography continues to advance and more stringent demands need to be met by the copying apparatus in order to increase performance standards, and to obtain high quality images. Additionally, photoresponsive devices are desired which can be charged positively, and contain therein an electron transporting material.
Recently, there has been disclosed layered photoresponsive devices comprised of photogenerating layers and transport layers as described in U.S. Pat. No. 4,265,990, and overcoated photoresponsive materials containing a hole injecting layer, in contact with a transport layer, an overcoating of a photogenerating layer, and a top coating of an insulating organic resin, reference, for example, U.S. Pat. No. 4,251,612. Examples of generating layers disclosed in these patents include trigonal selenium, and phthalocyanines, while examples of transport layers that may be used, which layers transport positive charges, in contrast to the transport layers of the present invention which transport electrons, include certain diamines dispersed in a resinous binder. The disclosure of each of these patents, namely U.S. Pat. Nos. 4,265,990 and 4,251,612 are totally incorporated herein by reference.
Many other patents are existence describing photoresponsive devices including layered devices containing generating substances such as U.S. Pat. No. 3,041,167, which discloses an overcoated imaging member containing a conductive substrate, a photoconductive layer, and an overcoating layer of an electrically insulating polymeric material. This member is utilized in an electrophotographic copying by, for example, initially charging the member with electrostatic charges of a first polarity, and imagewise exposing to form an electrostatic latent image, which can be subsequently developed to form a visible image. Prior to each succeeding imaging cycle, the imaging member can be charged with an electrostatic charge of a second polarity which is opposite in polarity to the first polarity. Sufficient additional charges of the second polarity are applied so as to create across the member a net electrical field of the second polarity. Simultaneously, mobile charges of the first polarity are created in the photoconductive layer by applying an electrical potential to the conductive substrate. The imaging potential which is developed to form the visible image is present across the photoconductive layer, and the overcoating layer.
Furthermore, there is disclosed in U.S. Pat. No. 4,135,928 electrophotographic light sensitive members containing 7-nitro-2-aza-9-fluorenylidene-malononitrile as a charge transporting substance. According to the disclosure of this patent, the electrophotographic light sensitive members contain an electroconductive support, a layer thereof comprising a charge generating substance, and 7-nitro-2-aza-9-fluorenylidene-malononitrile, of the formula, for example, as illustrated in column 1.
Other representative patents disclosing layered photoresponsive devices include U.S. Pat. Nos. 4,115,116, 4,047,949, and 4,315,981. There is disclosed in the '981 patent an electrophotographic recording member containing an organic double layer. According to the disclosure of this patent, the recording member consists of an electroconductive support material and a photoconductive layer of organic materials which contain a charge carrier producing dyestuff layer of a compound having an aromatic or heterocyclic polynuclear quinone ring system, and a transparent top layer of certain oxdiazoles. Apparently, this recording member is useful in electrophotographic copying processes where negative charging of the top layer occurs when an electron donating compound is selected for the device involved.
Many of the photoresponsive devices described, such as those disclosed in U.S. Pat. No. 4,265,990, contain a transport layer, the function of which is to transport positive charges generated by the photogenerating layer. In the imaging sequence, these devices are charged negatively thus necessitating the need for a charge carrier transport material which will allow the migration of positive charges. Similar devices containing electron transporting layers are relatively unknown.
Thus, while the above described photoresponsive devices are suitable for their intended purposes, there continues to be a need for improved devices, particularly layered devices which can be repeatedly used in a number of imaging cycles without deterioration thereof from the machine environment or surrounding conditions. Additionally, there continues to be a need for improved layered imaging members which contain electron transporting layers, thus allowing such devices to be positively charged. Moreover, there continues to be a need for improved photoresponsive devices which can be prepared with a minimum number of processing steps, and wherein the layers are sufficiently adhered to one another to allow the continuous use of these devices in repetitive imaging and printing systems. Furthermore, there continues to be a need for improved photoresponsive layered devices.